Engine ground system

ABSTRACT

An engine ground system for increasing the potential of an engine. This is an engine ground system wherein intermediate portions of a ground wire one end of which is electrically connected to the negative electrode terminal of a battery are electrically connected to engine ground points and the other end of the ground wire is grounded to the car body. The engine ground points can be an engine cylinder head, an intake manifold clamping member, a cylinder head cover, and a throttle body ( 7   b ). Further, a plug cap ground wire is connected between the plug cap clamping member and the intake manifold clamping member.

BACKGROUND OF THE INVENTION

The present invention relates to an engine ground system, for example,to an engine ground system that decreases the electric resistance,smooths the flow of electric current, and improves performancecharacteristics of the engine by directly grounding the ground points ofthe automotive engine carrying a direct ignition coil of an internaligniter type to a negative electrode terminal of a battery via a groundwire.

A variety of measures have been taken to improve output performance ofengines installed on automobiles. For example, a spark tuning system wasdisclosed in which a mixture inside the combustion chamber of the enginewas brought closer to a complete combustion state by connecting thespark plugs by a wire harness having a specific structure and conductingspark tuning of the spark plugs. The applicant has also employed such aspark tuning system in practice. With this technology, engine output isincreased by conducting optimum control of the electric current valueinputted to the positive electrode terminal side of the spark plug in astate prior to spark plug discharge. On the other hand, the developmentof a ground system for controlling the minus electric current after aspark plug discharge, that is, after the spark plugs have beenactivated, is also required.

In the conventional ground system for automobiles, the electric currentof a power source is supplied from the positive electrode terminal of abattery to a variety of electric devices such as electronic controldevices carried by the automobile, spark plugs, stator motor,instruments on an instrument panel, illumination devices such as lamps,and acoustic devices. Further, after flowing through the electricdevices, the electric current flowed through a ground wire connected tothe vehicle body and returned to the negative terminal of the battery.As a result, wiring of the wire hardness for electrically connectingvarious electric devices and the battery was simplified. However,vehicle bodies are usually formed by using steel sheets. Therefore, theconductivity thereof is about one tenth that of copper used for the wireharness, and when the vehicle body is employed for grounding, electricresistance is high. As a result, there is an adverse effect on the sparksystem of the engine and the engine is greatly hindered from exhibitingits full potential. Another problem is that when the intake flow passesinside the throttle device of an engine intake system, intake airfriction causes static electricity, which creates noise hindrance forsignal wires of acoustic devices wired in the engine compartment.

Accordingly, the applicant has conducted research and development of anengine ground system for improving the output characteristics of anengine based on the knowledge obtained with the spark plug tuning systemthat has been heretofore disclosed. As a result, new technology bringingout an engine's full potential has been created.

Thus, with the foregoing in view, it is an object of the presentinvention to provide an engine ground system that increases an engine'spotential by causing the minus electric current after the spark plugdischarge to flow smoothly to the ground wire using a constitutionwherein the intermediate positions on the ground wire wired between thenegative electrode terminal of the battery and the vehicle body areconnected to a cylinder head, which is the ground point of the engine,or to a plug cap of a direct ignition coil via this cylinder head.

SUMMARY OF THE INVENTION

The inventors have created the following inventions to resolve theabove-described problems.

Thus, the invention of claim 1 relates to an engine ground system inwhich intermediate positions on a ground wire electrically connected byone end thereof to a negative electrode terminal of a battery areelectrically connected to ground points of the engine and then the otherend of the ground wire is grounded to the vehicle body, wherein theground point of the engine is set on the cylinder head of the engine.

When the above-described configuration is employed, the minus current onthe negative electrode side during a spark in a spark plug smoothlyflows to the negative electrode terminal via the ground wire from theground point provided on the cylinder head. As a result, theelectromotive force induced in the ignition coil on the secondary sideis increased and spark performance is greatly improved.

Another aspect of the invention relates to an engine ground system inwhich intermediate positions on a ground wire electrically connected byone end thereof to a negative electrode terminal of a battery areelectrically connected to ground points of the engine and then the otherend portion of said ground wire is grounded to the vehicle body, whereinthe ground points of the engine are the cylinder head of the engine anda clamping member for an intake manifold for clamping the intakemanifold to the cylinder head.

With such a configuration, an additional effect is that the minuscurrent of the spark plug also flows from the clamping member for theintake manifold to the negative electrode terminal of the battery viathe ground wire and spark characteristics are further improved.

Another aspect of the invention relates to an engine ground system inwhich intermediate positions on a ground wire electrically connected byone end thereof to a negative electrode terminal of a battery areelectrically connected to ground points of the engine and then the otherend of the ground wire is grounded to the vehicle body, wherein theground points of the engine are the cylinder head of the engine, aclamping member for an intake manifold for clamping the intake manifoldto the cylinder head, and a cylinder head cover.

With such a configuration, an additional effect is that the minuscurrent of the spark plug also flows from the cylinder head cover,thereby accordingly improving the accuracy of ground tuning.

Another aspect of the invention relates to an engine ground system inwhich intermediate positions on a ground wire electrically connected byone end thereof to a negative electrode terminal of a battery areelectrically connected to ground points of the engine and then the otherend portion of said ground wire is grounded to the vehicle body, whereinthe ground points of said engine are the cylinder head of the engine anda clamping member for an intake manifold for clamping the intakemanifold to the cylinder head, a cylinder head cover, and a throttlebody.

With such a configuration, because the throttle body is also made aground point, static electricity generated on the throttle body can beremoved. As a result, a smooth flow of minus electric current of thespark plugs to the negative electrode terminal of the battery can beimplemented, the spark performance of the spark plugs is furtherimproved, and the hindrance of acoustic devices by noise induced bystatic electricity can be avoided.

According to another aspect of the invention, spark means provided inthe engine has a direct ignition coil of an internal igniter type andthe other end of the ground wire for a plug cap electrically connectedby one end thereof to the plug cap accommodating the direct ignitioncoil is electrically connected to the clamping member for an intakemanifold.

With such a configuration, the ground wire for the plug cap is providedso as to connect the plug cap accommodating the direct injection coiland the clamping member for the intake manifold. Therefore, the minuselectric current of the spark plug flows directly from the plug cap tothe ground wire for the plug cap, the electric resistance toward thenegative electrode terminal of the battery is accordingly decreased, andthe spark performance of the spark plug is improved.

Another aspect of the invention relates to the engine ground systemdescribed immediately hereinabove, wherein the one end of the groundwire for a plug cap is connected to the clamping member for the plug capfor clamping the plug cap to the cylinder head.

According to another aspect of the invention, one end of the ground wirefor a plug cap is connected to the clamping member for the plug capwhich is screwed into the cylinder head of the engine. Therefore, theminus current of the spark plug flows to the ground wire for the plugcap with higher reliability.

According to another aspect of the invention, a negative electrodeterminal of the battery to which the other end of the ground wire iselectrically connected is grounded to the vehicle body via anotherground wire different from the aforementioned ground wire.

With such a configuration, in addition to the ground wire, a separateground wire is electrically connected to the negative electrode terminalof the battery. Therefore, the wiring of the ground wire is simplified.

According to another aspect of the invention, the ground wire and theground wire for a plug cap have a four-layer structure comprising, fromthe core portion thereof, a core wire composed of bundled twisted wiresformed by twisting fine copper wires, an inner coating member, which isa synthetic resin material coated on the outer periphery of the corewire, a wire mesh, which is an electrically conductive material providedso as to cover the outer periphery of the coating material, and an outercoating member, which is a synthetic resin material provided on theouter periphery of the wire mesh.

With such configuration, the core wire of the ground wire or the groundwire for a plug cap having a four-layer structure is formed from acopper material and demonstrates an ultra-low resistance. As a result,the minus current generated in the spark plugs can smoothly flow to thenegative electrode terminal of the battery. Furthermore, because thecore wire is covered with the wire mesh, electromagnetic waves emittedfrom the engine compartment to the outside environment can bereliability shielded, and noise generated in the electronic controlequipment for the engine and hindrance such as noise in the audioequipment can be effectively avoided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an external perspective view showing the inside of the enginecompartment of an embodiment of the present invention.

FIG. 2 is an external perspective view showing the cross-sectionalstructure of a wire harness.

FIG. 3 is an external perspective view showing the first ground wire,second ground wire, and ground wire for a plug cap constituting theground system of the engine shown in FIG. 1.

FIG. 4 is an output performance graph illustrating the relationshipbetween power, torque, and time before the ground mounting.

FIG. 5 is an output performance graph illustrating the relationshipbetween power, torque, and time after the ground mounting.

FIG. 6 is a graph illustrating the spark waveform obtained with anoscilloscope before the ground mounting.

FIG. 7 is a graph illustrating the spark waveform obtained with anoscilloscope after the ground mounting.

FIG. 8 represents data illustrating the luminosity measurement results,(a) is the data table, (b) is a graph illustrating how the data table isplotted as a graph.

FIG. 9 is a graph representing the output measurement results showingthe relationship between the output and speed of vehicle A.

FIG. 10 is a graph representing the output measurement results forvehicle B, similarly to FIG. 9.

FIG. 11 is a fuel consumption at steady speed graph in which the testresults on fuel consumption at steady speed are represented by therelationship between the fuel consumption and speed.

FIG. 12 is a start acceleration graph showing the results obtained in astart acceleration test.

FIG. 13 is a graph showing the results of a passing acceleration testconducted on vehicle A.

FIG. 14 is a graph showing the results of a passing acceleration testsimilarly conducted on vehicle B.

FIG. 15 relates to output measurement results obtained for vehicle C;this figure is a graph showing the relationship between torque andengine rpm.

FIG. 16 relates to output measurement results obtained for vehicle C;this figure is a graph showing the relationship between output andengine rpm.

FIG. 17 relates to the results of a power performance test conductedwithout mounting the ground system on vehicle C and represents a graphshowing the relationship between engine rpm and torque, where engine rpmis plotted against the abscissa and torque is plotted against theordinate.

FIG. 18 relates to the results of a power performance test conductedwithout mounting the ground system on vehicle C and represents a graphshowing the relationship between engine rpm and output, where engine rpmis plotted against the abscissa and output is plotted against theordinate.

FIG. 19 relates to the results of a power performance test conducted onvehicle C with the mounted ground system, but in a mode in which noground connection is made to the throttle body and represents a graphshowing the relationship between engine rpm and torque, where engine rpmis plotted against the abscissa and torque is plotted against theordinate.

FIG. 20 relates to the results of a power performance test conducted onvehicle C with the mounted ground system, but in a mode in which noground connection is made to the throttle body and represents a graphshowing the relationship between engine rpm and output, where engine rpmis plotted against the abscissa and output is plotted against theordinate.

FIG. 21 relates to the results of a power performance test conducted onvehicle C in a ground system mode in which the throttle body was alsogrounded and represents a graph showing the relationship between enginerpm and torque, where engine rpm is plotted against the abscissa andtorque is plotted against the ordinate.

FIG. 22 relates to the results of a power performance test conducted onvehicle C in a ground system mode in which the throttle body was alsogrounded and represents a graph showing the relationship between enginerpm and output, where engine rpm is plotted against the abscissa andoutput is plotted against the ordinate.

FIG. 23 is a table showing the maximum torque values and maximum outputvalues of FIGS. 17 to 22.

DETAILED DESCRIPTION OF THE INVENTION

The embodiments of the present invention will be described in detailhereinbelow with reference to FIG. 1 through FIG. 3. FIG. 1 is aperspective external view of an engine compartment 1, as seen by aperson standing on the front bumper looking down at the enginecompartment 1 of a car of the present embodiment. As shown in FIG. 1, anengine 2 transversely disposed in the engine compartment 1 is, forexample, a four-cylinder ignition engine. In a cylinder head 2 athereof, a cavity accommodating a spark plug is formed in each cylinder.The spark plugs are accommodated and fixed by screwing into the cylinderhead 2 a. Further, a plug cap 3 accommodating an internal igniter typedirect ignition coil is detachably provided on the positive electrodeterminal of the head portion of each spark plug facing outwardly fromthe spark plug fixed to the cylinder head cover 2 b. This directignition coil represents an ignition system that does not use a plugcord, prevents the current loss or noise arising when a plug cord isused, and directly provides a secondary current to the ignition plug bya primary current of the igniter. Therefore, the ignition timing, forexample, can be obtained by detection with a crank sensor of the engine,computer processing in combination with information from a fuelinjection device, and electronic control.

Furthermore, an intake manifold 4 is clamped and fixed to the sidesurface of the cylinder head 2 a with a bolt 4 a which is a clampingmember for the intake manifold. Each cylinder (not shown in the figure)is so formed that external air taken into an air cleaner 5 passesthrough a suction duct 6 and throttle device 7 and is then supplied fromthe intake manifold 4.

A first ground wire 10 and a second ground wire 11 (separate groundwire), which are electrically connected respectively to a left struttower (automobile body, may be a fender panel or inner liner) 1 a and aright strut tower (automobile body, may be a fender panel or innerliner) 1 b forming the engine compartment 1, are electrically connectedto a negative electrode terminal 8 a of a battery 8. Such a wiringprovides for grounding to both the first ground wire 10 and secondground wire 11, as well as the negative electrode terminal 8 a of thebattery 8 and left and right strut towers 1 a, 1 b.

The structure of a wire harness 12 used for the above-described firstground wire 10, second ground wire 11 and the below described groundwire 100 for a plug cap will be described hereinbelow with reference toFIG. 2. The wire harness 12 used for the ground system of the engine ofthe present embodiment has a four-layer structure in which a core wire12 a of the central portion is formed by seven twisted wires 120 a. Eachtwisted wire 120 a is obtained, for example by twisting a bundle of 211copper wires with a diameter of 0.12 Ø and a high purity (99.9%),thereby ensuring a high electric conductivity. The surface of the copperwires is subjected to oxidation-preventing treatment to protect fromcorrosion. The core wire 12 a is covered on the outside with an innercoating member 12 b which is a synthetic resin material, for example,polyvinyl chloride or a polyolefin, to reduce noise and ensure strength.The outer periphery of the inner coating member 12 b is covered with awire mesh 12 c from an electrically conductive material, for example,brass, as a shield for preventing electromagnetic waves from leaking tothe outside. An outer coating member 12 d, which is a synthetic resinmaterial with high heat resistance and bendability, is covered on theouter periphery of the wire mesh 12 c. The wire harness 12 thus has as awhole a four-layer structure, and a cable 12 (wire harness) with greatlyreduced electric resistance is thus formed.

The structure of the first ground wire 10 and second ground wire 11 usedin the ground system of the engine will be explained below withreference to FIG. 1 through FIG. 3. The first ground wire 10 and secondground wire 11 use the above-described wire harness 12 and are crimpedtogether with battery metal terminals 10 a connected to the negativeelectrode terminal 8 a of the battery 8, thereby forming continuousground wires. In addition to the aforementioned battery metal terminal10 a, crimped to the first ground wire are a throttle metal terminal 10b for connection to the throttle body 7 b of the throttle device 7, acylinder head metal terminal 10 c for connection to the cylinder head 2a, an intake manifold metal terminal 10 d (two in the presentembodiment) for connection to the clamping member 4 a for the intakemanifold, a cylinder head cover metal terminal 10 e for connection tothe cylinder head cover 2 b, and a strut metal terminal 10 f forconnection to the left strut tower 1 a. The wire harnesses 12 areintegrally and continuously connected in those terminals 10 b–10 e.Further, the second ground wire 11 joined by integrally crimping in thebattery metal terminal 10 a is joined at the free end thereof bycrimping the strut metal terminal 11 a connected to the right struttower 1 b.

Further, four ground wires 100 for plug caps are provided in the firstground wire 10. Each ground wire 100 for a plug cap has attached bycrimping to one end thereof a plug cap metal terminal 100 a for electricconnection to each plug cap 3, and to the other end thereof a manifoldmetal terminal 100 b for electric connection to the bolt 4 a which is anintake manifold clamping member. Thus, each two adjacent ground wires100 for plug caps form a pair and are integrally crimped and connectedwhen crimped with the manifold metal terminal 100 b and are formed so asto fork into two branches from the manifold metal terminal 100 b.Further, the ground wires 100 for plug caps are electrically connectedto the first ground wire 10 by clamping the manifold metal terminal 100b with the intake manifold metal terminal 10 d via the bolt 4 a.

In the figures, the reference symbol 8 b stands for a positive electrodeterminal of the battery 8, and 13 for a ground wire serving as vehicleminus wiring. The positive electrode terminal 8 b is connected to theelectric devices serving as an electric load. The ground wire 13 servingas the vehicle minus wiring is electrically connected together with thebattery terminal 10 a to the negative electrode terminal 8 a by using aterminal extension tool (not shown in the figures). Further, thereference symbols 1 c and 1 d denote the holes for bolts drilled in theleft and right strut towers 1 a, 1 b, and 7 a denotes a bolt holedrilled in the body 7 b of the throttle device 7.

The attachment of the first ground wire 10 and second ground wire 11will be explained. As for the first ground wire 10, the battery metalterminal 10 a is connected together with the vehicle ground wire 13 tothe negative electrode terminal 8 a of the battery 8 by using theterminal extension tool (not shown in the figure). The left strut metalterminal 10 f is grounded together with the provided ground wire for aheadlight (not shown in the figure) to the vehicle body by inserting theprovided bolt into the bolt hole 1 c. Similarly, the right strut metalterminal 11 a of the second ground wire 11 is also grounded togetherwith the ground wire (not shown in the figure) for the providedheadlight to the vehicle body by screwing the provided bolt (not shownin the figure) into the bolt hole 1 d.

Thus the engine ground system is formed by electrically connecting tothe ground points provided at the engine 2 the intermediate positions onthe first ground wire 10 in which the battery metal terminal 10 a isclamped to the negative electrode terminal 8 a and the strut metalterminal 10 f is clamped to the left strut tower 1 a. Thus, the cylinderhead 2 a, bolt 4 a as a clamping member for the intake manifold,cylinder head cover 2 b, and body 7 b of the throttle device 7 are theground points provided on the engine.

The throttle metal terminal 10 b is thus connected to the throttledevice 7 with the bolt screwed into the bolt hole 7 a of the throttlebody 7 b.

The cylinder head metal terminal 10 c is connected together with theprovided ground wire (not shown in the figure) of the engine to thecylinder head 2 a with the provided bolt (not shown in the figure).

The intake manifold metal terminal 10 d is connected together with themanifold metal terminal 100 b of the ground wire 100 for a plug cap tothe intake manifold 4 by joint clamping with the bolt 4 a.

The cylinder head cover metal terminal 10 e is connected to the cylinderhead cover 2 b with bolts 20 b (provided in an appropriate number ofplaces around the cylinder head cover 2 b) attaching the cylinder headcover 2 b to the cylinder head 2 a.

Further, the plug cap metal terminal 100 a of the ground wire 100 for aplug cap is attached and connected to a bolt (not shown in the figure)for a plug cap serving to position and fix the plug cap 3 to thecylinder head 2 b.

Therefore, in the embodiment having the above-described configuration,the first ground wire 10, ground wire 100 for a plug cap, and secondground wire 11 use the wire harness 12 having excellent electricconductivity and a low electric resistance, intermediate positions ofthe first ground wire 10 formed of this wire harness 12 are connected toground points of the engine, and those ground points are electricallyconnected to the negative electrode terminal 8 a of the battery 8 viathe first ground wire 10. Therefore, during engine operation, the minuselectric current generated on the negative electrode side of the sparkplug smoothly flows directly to the negative electrode terminal 8 a ofthe battery via the first ground wire 10, thereby improving engineperformance. Thus, various effects are obtained including increase intorque in a low-speed and medium-speed range of the engine, increase infuel efficiency, increase in start performance of the engine, improvedpurification of exhaust gases by complete combustion, increase inillumination degree of the headlamp, and noise reduction in audioequipment of various types.

The results of the performance tests conducted by the applicant will bedescribed below in greater detail.

First, the performance evaluation test of spark plugs will be explainedbased on FIG. 4 and FIG. 5. The performance evaluation test of sparkplugs was conducted with respect to a case where the first ground wire10 was connected by setting the cylinder head 2 a as the ground point ofthe engine at an intermediate position of the first ground wire 10, thatis, with respect to a case where the cylinder head metal terminal 10 cwas electrically connected to the cylinder head 2 a (such a case shallbe referred to as “after the ground mounting”) and a case where such afirst ground wire 10 was not present (such a case shall be referred toas “before the ground mounting”). In this performance evaluation test ofspark plugs, the primary electric current of the spark of the sparkplug, power (PC), and torque (kg-m) before and after ground mountingwere simultaneously measured and compared. In order to reproduce thestate during vehicle movement, measurements were conducted with a loadapplied. As for the measurement conditions, in a speed mode reproducingthe loaded state, a dynamo was used, the dynamo settings were such as tofix the engine rotation speed at 4000 rpm, the accelerator wascompletely opened, and the measurements were conducted with the speedset to 4000 rpm.

As a result, as shown in FIG. 4, a performance graph illustrating therelationship between power, torque, and time before the ground mounting,and as shown in FIG. 5, the performance graph showing the relationshipbetween power, torque, and time after the ground mounting were obtained.In each graph, the “measurement point” was the point in time in whichthe prescribed interval has elapsed since the rotation speedfluctuations have stabilized after the engine rotation speed had reached4000 rpm. In FIG. 4 and FIG. 5, after the ground mounting, the power wasfound to increase by 104−99=5 (PS) and the torque was found to rise by18.4−17.7=0.7 (kg-m) with respect to those before the ground mounting.

Furthermore, FIG. 6 and FIG. 7 show the graphs representing the sparkwaveform obtained with an oscilloscope as the waveforms of the sparkprimary, current of the spark plug at this time. According to thosegraphs, the spark primary current increased by 8.64−8.56=0.08 (A) and itwas found that the fall time (that is, the time until the output currentdrops to zero) was reduced by 17.7−11.8=5.9 (μs). Because the currentvalue and time relate to the primary side, the electromotive force Einduced on the secondary side by the mutual induction is represented byE=M(i/t). Here, M stands for mutual inductance, t stands for time, and istands for electric current. Because the mutual inductance M does notchange, from this formula, the electromotive force En in the case beforethe ground mounting becomes En=M(8.56 A/17.7 μs)=483615.8 M and theelectromotive force Eh in the case after the ground mounting becomesEh=M (8.64 A/11.8 μs)=73223.4 M. From here it follows that Eh=1.5 En.Therefore, it was clarified that with the engine ground system, afterthe ground mounting, an electromotive force has been generated that isabout 1.5 times that of the usual state before the ground mounting. Asfollows from the comparison of data shown in FIG. 4 and FIG. 5, thepower increased by 5 PS and the torque increased by 0.7 kg-m apparentlybecause the generated electromotive force increased by a factor of 1.5.

Thus, employing the engine ground system of the present embodiment makesit possible to cause the minus current of the spark plug to flowsmoothly to the negative electrode terminal 8 a of the battery 8 via thefirst ground wire 10. As a result, the spark performance of the sparkplug is greatly increased and, therefore, engine performance isimproved.

Furthermore, various performance evaluation tests were conducted inaddition to the above-described spark performance test. The resultsthereof will be described below. The below-described tests wereconducted on vehicle A and vehicle B of different types, that is, havingdifferent weight and carrying different engines.

The luminosity measurement results will be explained below based on FIG.8. FIG. 8 shows the luminosity measurement results obtained by a benchtest conducted by using a headlight test; figure (a) is a table showingthe luminosity measurement data, (b) is a graph representing datadescribed in the table. Those data demonstrated that the luminosity ofthe headlight after the ground mounting has increased over that beforethe ground mounting for both the vehicle A and the vehicle B. From this,it follows that the increase in luminosity is due to the fact that theground wire for a headlight is connected at the strut towers 1 a, 1 b tothe first ground wire 10 and second ground wire 11 formed in the wirehardness 12 with a four-layer structure having a core wire 12 a withexcellent electric conductivity as a center.

The output measurement results will be explained with reference to FIG.9 and FIG. 10. FIG. 9 and FIG. 10 show the results obtained in measuringthe engine output with a chassis dynamo tester. FIG. 9 is a graphshowing output measurement results relating to vehicle A, and FIG. 10 isa graph showing output measurement results relating to vehicle B. In thecase of vehicle A, the point in time with a speed of 180 km/h duringmaximum output generation was taken as the measurement point, and in thecase of vehicle B, the point in time with a speed of 110 km/h duringmaximum output generation was taken as the measurement point. Resultsshowed that in the vehicle A, the output after the ground mountingincreased by 2.5% over that before the ground mounting, and in the caseof vehicle B, the output also increased by 2.0%. Thus, it was found thatemploying the ground system resulted in a significant increase in engineoutput.

FIG. 11 illustrates measurement results relating to fuel consumption atsteady speed determined by an actual vehicle running test. The fuelconsumption at steady speed is determined by measuring the fuelconsumption (km/L) when the vehicle runs at a constant speed from 40km/h to 100 km/h, with intervals of 20 km/h in a test in which thevehicle runs at a constant speed on a horizontal straight road. As aresult, as shown in FIG. 1, a fuel consumption at steady speed graphbased on the fuel consumption at steady speed measurement data wasobtained. A significant improvement of fuel consumption of 17.16% and11.52% on average was obtained by employing the ground system in vehicleA and vehicle B, respectively. Thus, the ground system can improve fuelconsumption.

FIG. 12 illustrates the measurement results relating to accelerationfrom standstill performance. The measurement conditions were as follows.A vehicle was running on a horizontal road and a contactless five-wheelmeasurement device was used to measure acceleration determined by timerequired for the vehicle to travel from 0 to 400 m. As a result, theacceleration from standstill graph shown in FIG. 12 was obtained. Thus,when the time required to reach 400 m was measured, it was found thatemploying the same ground system made it possible to shorten this timeby 0.15 sec for vehicle A and by 0.64 sec for vehicle B with respect tothe cases where no ground system was employed. Therefore, employing theground system can increase the acceleration when the vehicle startsmoving.

The measurement results relating to passing acceleration performancewill be explained below with reference to FIG. 13 and FIG. 14. Theresults shown in FIG. 13 and FIG. 14 were obtained by measurements witha contactless five-wheel measurement device. The time required toincrease the speed by 20 km/h from a standard speed, that is, from 40km/h to 60 km/h and from 60 km/h to 80 km/h, was measured. FIG. 13 showsa passing acceleration graph relating to vehicle A, and FIG. 14 shows apassing acceleration graph relating to vehicle B. Both the vehicle A andthe vehicle B could reach the prescribed speed within a shorter intervalafter the ground mounting then before the ground mounting. Therefore,excellent passing acceleration is demonstrated.

FIG. 15 and FIG. 16 show results relating to power performance obtainedby conducting measurements with respect to a third vehicle (referred tohereinbelow as “vehicle C”) that is different from the above-describedvehicle A and vehicle B. FIG. 15 shows a rpm-torque diagram illustratingthe relationship between the engine rpm and torque, and FIG. 16 shows arpm-output diagram illustrating the relationship between the engine rpmand output (PS). A comparative test was conducted with respect to thecase where a ground system shown in FIG. 1 was employed in a mode inwhich the ground wire 100 for a plug cap was not attached (such a casewill be referred to as “after the ground mounting”) and the case with anormal mode where such a ground system was not used at all (such a casewill be referred to as “before the ground mounting”). Results show that,as shown in FIG. 15, in the entire rpm range of the engine, the torquewas much higher when the ground system was employed (after the groundmounting) than when the ground system was not employed (before theground mounting). Furthermore, FIG. 16 demonstrates that the start-endoutput after the ground mounting increased from before the groundmounting. Those results demonstrated that in vehicle C, too, the powerperformance improved due to the employment of the ground system.

The results of the power performance test shown in FIGS. 17 to 23 willbe described. In the case of the vehicle C, the measurement conditionswere such that the test was conducted with respect to the ground systemin a mode in which the ground wire 100 for a plug cap was not attached.As for the measurement conditions in the test illustrated by FIGS. 17 to23, as shown in FIG. 1, a ground system was employed in which the groundwire 100 for a plug cap was employed, but the performance comparisontest was conducted separately for two sets of measurement conditions:with the ground system in a mode where the throttle metal terminal 10 bwas not connected to the throttle device 7 and the ground system in amode where the throttle metal terminal 10 b was connected. The testproduced a graph representing the relationship between engine rpm andtorque, in which engine rpm (rpm) was plotted against the abscissa andtorque (kg-m) was plotted against the ordinate, as shown in FIG. 17,FIG. 19, and FIG. 21, and a power performance graph in which engine rpmwas plotted against the abscissa and output was plotted against theordinate, as shown in FIG. 18, FIG. 20, and FIG. 22. Further, FIG. 23shows a table containing the maximum values represented in those FIGS.17 to 22.

Thus, as shown in FIG. 17, when no ground system was mounted, themaximum value of torque was T1=26.97 (kg-m), and the maximum value ofoutput was P1=229.3 (PS), as shown in FIG. 18. In a mode in which theground system was mounted, but the ground was not connected to thethrottle body 7 b, the maximum torque value was T2=27.01 (kg-m) fromFIG. 19 and the maximum output value was P2=233.7 (PS) from FIG. 20.Furthermore, in the case of the ground system shown in FIG. 1, that is,the ground system in which the throttle body 7 b was also grounded, thefollowing measurement results were obtained: the maximum torque valueT3=27.82 (kg-m), as follows from FIG. 21, and the maximum output valueP3=236.6 (PS), as follows from FIG. 22.

As follows from the table shown in FIG. 23, which represents theabove-described values of the maximum torque and maximum output, themaximum torque values (T2, T3) and maximum output values (P2, P3)obtained when the engine was driven in a mode with the mounted groundsystem were higher than the maximum torque value T1 and maximum outputvalue P1 obtained when the engine was driven in a mode without themounted ground system. Therefore, the power performance of the enginewith the mounted ground system was found to be improved. Further, evenwhen the ground system was mounted, the maximum torque value T3 andmaximum output value P3 obtained with grounding were larger than themaximum torque value T2 and maximum output value P2 obtained when thethrottle body was not grounded. Accordingly it was decided that theengine with the ground system which grounds the throttle body 7 b issuperior in terms of power performance.

In the above-described embodiment, the ground points on the engine sidewere the cylinder head 2 a, clamping member (bolt 4 a) for the intakemanifolds, cylinder head cover 2 b, and body 7 b of the throttle device7. In addition, for example, the transmission or surge tank provided inthe intake system may be set as a ground point, and an increase in thenumber of ground points is advantageous in terms of spark performance ofthe spark plugs.

Further, in the above-described embodiment, the explanation wasconducted with respect to a case where a direct ignition coil was used,but it goes without saying that the application to a so-calledmechanical spark system using a distributor or the like is alsopossible.

Furthermore, in the above-described embodiment, the explanation wasconducted with respect to an automobile, but the present invention canbe also applied to a variety of engines used in outboard motors,bicycles, carts, snowmobiles, and the like.

The inventions with the above-described configuration demonstrate thebelow-described effect. The invention provides an engine ground systemin which intermediate positions on a ground wire electrically connectedby one end thereof to a negative electrode terminal of a battery areelectrically connected to ground points of the engine and then the otherend of said ground wire is grounded to the vehicle body, wherein theground point of the engine is the cylinder head of the engine.Therefore, the following effects are produced: the torque in thelow-speed and medium-speed range of the engine is increased, the fuelconsumption is improved, performance of various types such as the sparkperformance, initial performance of the engine, acceleration fromstandstill performance of the engine, and passing acceleration ofperformance is improved, exhaust gas is purified by complete combustion,the degree of illumination with the head lamp is increased, and noiselevel of various audio devices is reduced.

According to another aspect the invention, the clamping member for theintake manifold is added as the ground point. Therefore, the minuscurrent of the spark plug also flows from the clamping member for theintake manifold to the negative electrode terminal of the battery viathe ground wire and spark characteristics are further improved.

According to another aspect of the invention, the cylinder head cover isadded as a ground point. Therefore, in addition, the minus current ofthe spark plug also flows from the cylinder head cover, therebyaccordingly improving the accuracy of ground tuning.

According to another aspect of the invention, the throttle body is addedas a ground point. Therefore, static electricity generated on thethrottle body can be eliminated. As a result, the minus electric currentof the spark plugs can flow smoothly to the negative electrode terminalof the battery, the spark performance of the spark plugs is furtherimproved, the hindrance of acoustic devices by noise induced by staticelectricity can be avoided, and the performance of acoustic devices canbe maintained in a good state.

According to another aspect of the invention, spark means provided inthe engine has a direct ignition coil of an internal igniter type andthe other end of the ground wire for a plug cap electrically connectedby one end thereof to the plug cap accommodating the direct ignitioncoil is electrically connected to the clamping member for an intakemanifold. As a result, the ground wire for the plug cap is provided soas to connect the plug cap accommodating the direct injection coil andthe clamping member for the intake manifold, the minus electric currentof the spark plug flows directly from the plug cap to the ground wirefor the plug cap, the electric resistance toward the negative electrodeterminal of the battery is accordingly decreased, and the sparkperformance of the spark plug is improved.

According to another aspect of the invention, one end portion of theground wire for a plug cap is connected to the clamping member for theplug cap. Therefore, connecting one end portion of the ground wire for aplug cap to the clamping member for the plug cap, which is screwed intothe cylinder head of the engine, allows the minus current of the sparkplug to flow to the ground wire for the plug cap with higherreliability.

According to another aspect of the invention, a separate ground wireconnected to the negative electrode terminal of the battery is groundedto the vehicle body. Therefore, luminosity of lamps such as headlightsis increased.

According to another aspect of the invention, the ground wire and theground wire for a plug cap have a four-layer structure comprising, fromthe core portion thereof, a core wire composed of bundled twisted wiresformed by twisting fine copper wires, an inner coating member, which isa synthetic resin material coated on the outer periphery of the corewire, a wire mesh, which is an electrically conductive material providedso as to cover the outer periphery of said coating material, and anouter coating member, which is a synthetic resin material, provided onthe outer periphery of the wire mesh. Therefore, the core wire of theground wire or ground wire for the plug cap, which has a four-layerstructure, demonstrates an ultra-low resistance. As a result, the minuscurrent generated in the spark plug can flow smoothly to the negativeelectrode terminal of the battery. Furthermore, because the core wire iscovered with the wire mesh, electromagnetic waves emitted from theengine compartment to the outside environment can be reliabilityshielded, and noise generated in the electronic control equipment forengine and hindrance such as noise in the audio equipment can beeffectively avoided.

1. A ground system for an engine mounted in a vehicle body, comprising a ground wire having two ends, the ground wire being electrically connected by one of said ends thereof to a negative electrode terminal of a battery,intermediate positions on the ground wire being electrically connected to ground points of the engine and the other end of said ground wire being grounded to the vehicle body, the ground points of the engine comprising a ground point on a cylinder head of said engine.
 2. A ground system according to claim 1, wherein the ground points of said engine further comprise a clamping member for an intake manifold for clamping the intake manifold to the cylinder head.
 3. A ground system according to claim 2, wherein the ground points of said engine further comprise a cover of the cylinder head.
 4. A ground system according to claim 3, wherein the ground points of said engine further comprise a throttle body.
 5. The engine ground system according to any of claims 2 through 4, wherein spark means provided in said engine has a direct ignition coil of an internal igniter type accommodated in a plug cap, a ground wire for the plug cap, one end of the plug cap ground wire being electrically connected to the plug cap and the other end of the plug cap ground wire being electrically connected to said clamping member for an intake manifold.
 6. The engine ground system according to claim 5, wherein one end of said plug cap of said ground wire is electrically connected to a clamping member for clamping said plug cap to said cylinder head.
 7. The engine ground system according to any of claims 1 through 4, wherein the negative electrode terminal of said battery to which the other end portion of said ground wire is electrically connected is grounded to said vehicle body via another ground wire different from said ground wire.
 8. The engine ground system according to claim 5, wherein said ground wire and said ground wire for a plug cap each have a four-layer structure comprising a core wire comprised of bundled twisted wires formed by twisting fine copper wires, an inner coating comprising a synthetic resin material coated on an outer periphery of the core wire, a wire mesh comprising an electrically conductive material and covering an outer periphery of said coating material, and an outer coating comprising a synthetic resin material on an outer periphery of said wire mesh.
 9. The engine ground system according to claim 6, wherein said ground wire and said ground wire for a plug cap each have a four-layer structure comprising a core wire comprised of bundled twisted wires formed by twisting fine copper wires, an inner coating comprising a synthetic resin material coated on an outer periphery of the core wire, a wire mesh comprising an electrically conductive material and covering an outer periphery of said coating material, and an outer coating comprising a synthetic resin material on an outer periphery of said wire mesh. 